1. Field of the Invention
The present invention is directed to a method for identifying spikes which arise in MR signals obtained in nuclear magnetic resonance tomography.
2. Description of the Prior Art
Spike signals are occasionally present which disturb the measured values in nuclear magnetic resonance tomography. For example, spikes can arise due to electrostatic discharges or mains disturbances. Two or more spikes can already make an image diagnostically valueless, so that the entire measurement must be repeated. A number of methods were therefore developed for blanking unavoidable spikes out of the measured signals. Initially, there is the problem of identifying spikes as such. The most obvious way is to interpret signals whose amplitude exceeds the MR signal as spikes. However, all spikes cannot be acquired in this way since their amplitude can also lie in the region of the values for the MR signal. After the process of identification, the position of the spikes must be acquired and the disturbed samples must be replaced.
A number of methods have been proposed for solving the aforementioned problems. M. J. Sanz and E. M. Haacke, Journal of Magnetic Resonance Imaging, 2 P, 789, 1992, and Y. Kao and J. R. Mac Fall, Proceedings of the SMR 760, 1995 propose using information from a region of uniform material. C. R. Crawford et al, Proceedings SMR, 939, 1995, propose employment of a high-pass filter in order to identify unwanted signals. In the field of chromatography, this method was also proposed S. A. Berkowitz, Analytical Chemistry 58, 2571-2576, 1986.
The problem of separating spike signals from noise signals with adequate reliability, however, has not been satisfactorily solved in any of these methods.